Arc shield for use in projection welding

ABSTRACT

An arc shield is used in projection welding. The projection welding is performed for welding the lower end of a metal stud to the upper surface of a metal plate. The stud has a head and a stem connected securely to the central portion of the lower surface of the head. The arc shield includes an annular horizontal top wall defining a hole therein, and an annular vertical side wall having an annular top end connected securely to the outer peripheral portion of the top wall, and an annular bottom end having a plurality of notches. The annular side wall defines a chamber therein. The hole of the top wall has a size slightly greater than the diameter of the stem of the stud so as to allow for extension of the stem of the stud into the chamber through the hole of the top wall. When the projection welding is being performed, the electric arc is enclosed within the arc shield, while the surplus gas and molten metal that occur in the chamber flow from the arc shield through the notches of the annular side wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an arc shield for use in projection welding,which encloses the electric arc therein.

2. Description of the Related Art

In the architectural art, a metal stud is often used in projectionwelding to couple a steel member or a plurality of steel members with aconcrete layer. Referring to FIG. 1, a metal stud (1) is welded to anH-shaped steel member (3) and is embedded within a concrete layer (5).Referring to FIG. 2, in order to weld the lower end of the verticalcylindrical stem (1A) of the stud (1) to the upper surface of the topplate of the steel member (3), a generally semicircular metal filler(11) is attached to the lower end surface of the stem (1A) of the stud(1). A welding gun (2) holds the horizontal head (1B). When an electriccurrent is applied to the stud (1) from the welding gun (2), an electricarc is created between the stud (1) and the steel member (3).Accordingly, molten weld metal (12) is produced between the stud (1) andthe steel member (3). Solification of the molten weld metal (12) weldsthe stud (1) to the steel member (3).

Referring to FIG. 3, in order to weld a plurality of steel members (3')(only one is shown) to a concrete layer (not shown), a metal couplingplate (6) is provided so as to weld the steel members (3') thereto. Thecoupling plate (6) is coupled with the concrete layer by a stud (1') anda welding gun (2') in the same manner as the steel member (3) of FIG. 1.

The above-mentioned welding process suffers from the followingdisadvantages:

(1) If no arc shield is used, the electric arc may damage the eyes ofthe operator;

(2) When the operator holds an arc shield with one hand, it is difficultwith one-hand operation to accurately position the stud on the steelmember. Furthermore, it is time-consuming to perform this one-handoperation.

(3) Because the molten weld metal is exposed to the atmosphere duringwelding, dust may enter therein, thus forming bubbles in the solidifiedweld metal. The bubbles reduce the tensile strength of the solidifiedweld metal.

SUMMARY OF THE INVENTION

The main object of this invention is to provide an arc shield for use inprojection welding, which encloses the electric arc therein.

According to this invention, an arc shield is used in projectionwelding. The projection welding is performed for welding the lower endof a metal stud to the upper surface of a metal plate. The stud has ahead and a stem connected securely to the central portion of the lowersurface of the head. The arc shield includes an annular horizontal topwall defining a hole therein, and an annular vertical side wall havingan annular top end connected securely to the outer peripheral portion ofthe top wall, and an annular bottom end having a plurality of notches.The annular side wall defines a chamber therein. The hole of the topwall has a size slightly greater than the diameter of the stem of thestud so as to allow for extension of the stem of the stud into thechamber through the hole of the top wall. When the projection welding isbeing performed, the electric arc is enclosed within the arc shield,while the surplus gas and molten metal that occur in the chamber flowfrom the arc shield through the notches of the annular side wall.

Preferably, the top wall includes an annular neck projecting upwardtherefrom. The hole is formed through the neck. Accordingly, the lengthof the hole is increased so as to prevent the stud from moving relativeto the metal plate just before welding, thereby allowing for positioningof the stud on the metal plate.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of this invention will become apparent inthe following detailed description of a preferred embodiment of thisinvention, with reference to the accompanying drawings, in which:

FIG. 1 illustrates how a steel member is coupled with a concrete layer;

FIG. 2 illustrates how a metal stud is welded to a steel member;

FIG. 3 illustrates how a metal stud is welded to a coupling plate;

FIG. 4 is a perspective view of an arc shield according to thisinvention; and

FIG. 5 is a sectional view illustrating the use of the arc shield ofthis invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 4 and 5, an arc shield (4) of this invention is madeof metal and includes an annular horizontal top wall (41) and an annularvertical side wall (42) which has an annular top end connected securelyto the outer peripheral portion of the top wall (41), and an annularbottom end having twelve trapezoidal notches (421) each of which has ashorter upper side and a longer lower side. An annular neck (411)projects upward from the top wall (41). The side wall (42) defines acylindrical chamber (C) (see FIG. 5) therein. A hole (412) is formedthrough the assembly of the top wall (41) and the neck (411) and has asize slightly greater than the diameter of the stem (1A') of a standardmetal stud (1') (see FIGS. 3 and 5) so as to allow for extension of thestem (1A') through the hole (412).

Referring to FIG. 5, when the arc shield (4) is used in a so-called"projection welding" process for welding the stud (1') to a metalcoupling plate (6), to which a plurality of steel members (3') (only oneis shown) are welded, the stem (1A') of the stud (1') is insertedthrough the hole (412) of the arc shield (4). A generally semicircularmetal filler (11') , which is connected securely to the lower end of thestem (1A'), is placed at a selected position on the coupling plate (6)for welding. The head (1B') of the stud (1') is held on a welding gun(2'). When an electric current is applied to the stud (1') from thewelding gun (2'), an electric arc is produced between the stud (1') andthe lower end of the stem (1A') in the arc shield (4). The arc shield(4) can prevent dust from obtaining access to the molten weld metalformed between the stem (1A') and the coupling plate (6), thusincreasing the tensile strength of the solidified weld metal formedbetween the stem (1A' ) and the coupling plate (6). The increase in thetensile strength of the solidified weld metal has been proven by atensile test which has the following experimental data:

    ______________________________________                                        the diameter                                                                  of the stem                                                                            13 mm     16 mm     19 mm   22 mm                                    of the stud                                                                            (1/2")    (5/8")    (3/4")  (7/8")                                   ______________________________________                                        minimum  5400 kgf   8200 kgf 11600 kgf                                                                             15600 kgf                                load     (11905 lbf)                                                                             (18078 lbf)                                                                             (25574 lbf)                                                                           (34392 lbf)                              maximum  7400 kgf  11300 kgf 1500 kgf                                                                              21300 kgf                                load     (16314 lbf)                                                                             (24912 lbf)                                                                             (35053 lbf)                                                                           (46958 lbf)                              ______________________________________                                    

When the electric arc melts the weld metal, surplus gas and molten weldmetal, which occur in the chamber (C) of the arc shield (4), flow fromthe arc shield (4) through the notches (421) of the side wall (42). Whenthe gas discharge rate of the notches (421) is too great, it isdifficult to solidify the molten weld metal. If the gas discharge rateof the notches (421) is too small, bubbles are easily formed in thesolidified weld metal. In this embodiment, each of the notches (421) hasan upper side of 4.8 mm, a lower side of 3 mm and a height of 3.3 mm.Total area of the notches (421) is 154.44 mm² which falls in apermissible range.

Because the neck (411) projects from the top wall (41), the hole (412)of the arc shield (4) has a length sufficient to enable accuratepositioning of the lower end of the stem (1A') on the coupling plate (6)during the projection welding process.

With this invention thus explained, it is apparent that numerousmodifications and variations can be made without departing from thescope and spirit of this invention. It is therefore intended that thisinvention be limited only as indicated in the appended claims.

I claim:
 1. An arc shield for use in projection welding a lower end of ametal stud to an upper surface of a metal plate, said stud having a headand a stem connected securely to a central portion of a lower surface ofsaid head, said arc shield comprising:an annular horizontal top walldefining a hole therein, and an annular vertical side wall having anannular top end connected securely to an outer peripheral portion ofsaid top wall, and an annular bottom end including twelve trapezoidalnotches, said notches being defined by an upper side of approximately4.8 mm in length, a lower side of approximately 3.0 mm in length andhaving height of approximately 3.3 mm, said annular side wall defining achamber therein, said hole of said top wall having a size slightlygreater than a diameter of said stem of said stud so as to allow forextension of said stem of said stud into said chamber through said holeof said top wall, whereby, when said projection welding is beingperformed, electric arc is enclosed within said arc shield, whilesurplus gas and molten metal produced in said chamber flow from said arcshield through said notches of said annular side wall.
 2. An arc shieldas claimed in claim 1, wherein said top wall includes an annular neckprojecting upward therefrom, said hole being formed through said neck,whereby, length of said hole is increased so as to prevent said studfrom moving relative to said metal plate just before welding, therebyenabling accurate positioning of said stud on said metal plate.